Systems and methods for wireless link balancing in wireless networks

ABSTRACT

Systems and methods for controlling the transmit power and the receive sensitivity of an access point for achieving symmetric link balancing is described. When an access point operates with symmetric link performance, the access point does not inefficiently use available bandwidth for transmitting or re-transmitting to a client station that cannot communicate with the access point. Moreover, the access point does not back off transmissions due to activity of neighboring basic service sets when not needed. The receive sensitivity can be controlled using a hardware attenuator or software commands that adjust a programmable gain in a wireless local area network chipset used by the access point, or it can be controlled using adjustable levels in the software for processing or responding to packets.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/092,704, entitled “SYSTEMS AND METHODS FORWIRELESS LINK BALANCING IN WIRELESS NETWORKS,” filed Nov. 27, 2013,issuing as U.S. Pat. No. 9,467,953 on Oct. 11, 2016, which claims thebenefit of and/or the right of priority to U.S. Provisional PatentApplication No. 61/843,797 entitled “WIRELESS LOAD BALANCING IN WLANNETWORKS,” which was filed on Jul. 8, 2013; the contents of which areincorporated by reference in their entirety herein.

FIELD

The disclosed techniques relate to adjusting wireless link performanceof access points in a wireless local area network that has multipleaccess points.

BACKGROUND

The IEEE (Institute of Electrical and Electronics Engineers) 802.11hstandard defines a transmit power control (TPC) mechanism for reducinginterference between wireless networks by reducing the radio transmitpower of WLAN (wireless local area network) devices. TPC can also beused to manage power consumption of wireless devices and to adjust therange between access points and client stations.

When an access point sends frames of data to a client station, itspecifies whether TPC is supported, the maximum transmit power allowedin the WLAN, and the transmit power currently used by the access point.The transmit power used by client stations associated with an accesspoint are not permitted to exceed the maximum limit set by the accesspoint.

SUMMARY

Systems and methods for controlling the transmit power and the receivesensitivity of an access point in a wireless network for achievingsymmetric link balancing is described. When an access point operateswith symmetric wireless link performance, the effects are to push along-range client station to associate with and join a closer accesspoint to the client station, rather than a more distant access point; toallow many WLAN networks to coexist in one area; and to eliminate orreduce WLAN probe response traffic to long range clients and unnecessaryback offs due to the activity of overlapping basic service sets (BSSs)at a distance, thus, increasing the useful traffic sent between accesspoints and close-range client stations.

The receive sensitivity can be controlled using a hardware attenuatorfor adjusting the receiver gain. Alternatively, software commands can beused by a controller to adjust a programmable gain in a wireless localarea network chipset used by the access point.

Receiver thresholds that determine whether a packet is processed may bemodified to change the sensitivity of a receiver. For example, to detectthe beginning of IEEE 802.11 packets, an auto correlation or crosscorrelation function can be used and compared to a threshold, and thethreshold may be modified to change the receiver sensitivity.

A received packet may be ignored or not fully processed when thereceived power level of a packet is lower than a defined threshold. Forexample, when a probe request is received that has a power level lowerthan a defined value, it will not trigger a probe response. The samemethodology may be applied to an association request, a re-associationrequest, an authentication request, or other management or data packets.

Network allocation vector (NAV), a virtual carrier sensing mechanism,may not be held to apply to for packets that are lower than apredetermined power level. The energy detect (ED) threshold may also bemodified accordingly. The use of NAV and ED thresholds may be bypasssedso that the access point can transmit packets even when a client stationat a far distance is transmitting on the same channel to another accesspoint.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of a wireless link balancing system are illustrated in thefigures. The examples and figures are illustrative rather than limiting.

FIG. 1 shows devices that are part of an example WLAN (wireless localarea network).

FIG. 2 shows example asymmetric links for two access points, where thetransmit radius of an access point is different from the receive radiusfor that access point.

FIG. 3 shows example symmetric links for two access points, where thetransmit radius of an access point is substantially the same as thereceive radius for that access point.

FIG. 4A is a flow diagram illustrating an example process of determiningand setting receive sensitivity and transmit power.

FIG. 4B is a flow diagram illustrating an example process of an accesspoint re-adjusting its receive sensitivity.

FIG. 4C is a flow diagram illustrating an example process of a clientstation re-adjusting its receive sensitivity.

FIG. 5 shows the components of a wireless radio of an access point thathas transmit power control (TPC) adjustment capabilities.

FIG. 6 shows example components of a wireless radio of an access pointthat has both TPC adjustment capabilities and receiver sensitivityadjustment capabilities.

FIG. 7 depicts an architecture of an access point according to anembodiment of the present disclosure.

FIG. 8 is a flow diagram illustrating an example process of a controlleradjusting the transmit power and the receiver sensitivity of an accesspoint.

DETAILED DESCRIPTION

In an environment where there are multiple access points available for aclient station to associate with, the client station does notnecessarily associate with the closest access point. Moreover, even if aclient station initially associates with the closest access point, ifthe client station moves farther away from the access point, the clientstation may maintain an association with the original access point whenit is no longer the closest access point. In this situation, thebandwidth of the WLAN is not used efficiently by the access points andclient stations. Further, clients not associated with a close accesspoint may not achieve the throughput or the quality of service (QoS)that it may otherwise achieve when associating with the closest accesspoint.

FIG. 1 shows devices that are part of an example WLAN (wireless localarea network), such as may be found in an office building or apartmentcomplex. The WLAN includes multiple access points or base stations, AP1,AP2, AP3, and AP4. Each access point is coupled via a bus 115 tocontroller 110 and also wirelessly transmits signals to and receivessignals from client stations. The controller 110 can send TPC commandsas well as commands to adjust receiver sensitivity to each of the accesspoints.

As shown in FIG. 1, there can be multiple client stations, STA1, STA2,STA3, and STA4 in the WLAN environment. These client stations may beassociated with or seek to associate with one of the access points, AP1,AP2, AP3, and AP4. The access points and client stations exchange datawirelessly using a time division multiplexing (TDM) protocol.

Typically, the links between an access point and a client station areasymmetric, that is, the link budget for a transmission from the accesspoint to a client station and the link budget for a transmission in thereverse direction from the client station to the access point is not thesame. In particular, with the use of TPC to adjust the transmissionpower level of the access point, the asymmetry of the links can beexacerbated. For example, for an access point that has a transmit powerof +17 dBm and a receive sensitivity of −95 dBm, and for a clientstation that has a transmit power of +23 dBm and a receive sensitivityof −95 dBm, the access point to client station link budget is 112 dB(=+17 dBm+95 dBm), while the link budget for a client stationtransmission to the access point is 118 dB (=+23 dBm+95 dBm). In thiscase, there is a link budget asymmetry of 6 dB (118 dB-112 dB). For thisscenario, where the distance between the client station and the accesspoint is large enough that the client station is outside the range whereit can receive signals from the access point, the access point may stillbe capable of receiving signals from the client station.

Another way of looking at the link budget is to use the concepts oftransmit radius and receive radius. The transmit radius is the maximumdistance that the client station can be located from the access pointwhile still ensuring that the client station can receive signals fromthe access point, while the receive radius is the maximum distance thatthe client station can be located from the access point while stillensuring that the access point can receive signals from the clientstation. An access point has an asymmetric link performance with respectto a client station when its transmit radius and its receive radius arenot substantially the same. For access points that adhere to the IEEE802.11h protocol for TPC, adjustment of solely the transmit power canexacerbate the asymmetry in the wireless link of the access point.

Practically, one of the effects of an asymmetric link budget isinefficient use of the TDM system bandwidth. FIG. 2 shows exampleasymmetric link performance for AP1 and AP2. For both AP1 and AP2, thetransmit radius 202, 212 for transmission coverage is significantlysmaller than the respective receive radius 204, 214 for receptioncoverage. Because the transmit radius and the receive radius isdependent upon a particular client station's operating parameters, thetransmit radius 202, 212 and receive radius 204, 214 depicted in FIG. 2are example radii based upon a typical client station, for example, anApple iPhone®. Additionally, STA1 is within the transmit radius 202 andthe receive radius 204 of AP1, and STA2 is within the transmit radius212 and receive radius 214 of AP2, thus, no problems arise fromcommunications between AP1 and STA1 or from communications between AP2and STA2 due to the respective asymmetric link performance of AP1 andAP2.

However, if STA2 is connected to AP1, even though AP2 is closer, theasymmetric link performance for AP1 results in inefficient use of theTDM system bandwidth. This situation may arise if STA2 is initiallywithin the transmit radius 202 of AP1 and initially associates with AP1.Then if STA2 moves beyond the transmit radius 202 of AP1 but still stayswithin the receive radius 204 of AP1, as indicated by the location ofSTA2 in FIG. 2, transmissions sent by STA2 to AP1 are received by AP1,but transmissions from AP1 are not necessarily received by STA2.Consequently, AP1 may need to re-send transmissions more than once toSTA2, thus using additional wireless air bandwidth. The resulting datarate between AP1 and STA2 is lower than the potential communicationsdata rate that can be established between AP2 and STA2 because STA2 iswithin the transmit radius 212 of AP2, thus not requiring additionalbandwidth to be used in re-sending a transmission from AP2 to STA2.

FIG. 2 also shows that STA4 is located outside the transmit radius 202of AP1 but within the receive radius 204 of AP1, similar to thesituation with STA2. In this scenario, if STA4 is not already associatedwith AP1, a probe request from STA4 to associate with AP1 can reach AP1,but a probe response from AP1 cannot reach STA4. Then bandwidth iswasted by AP1 repeatedly attempting to send a probe response to STA4because STA4 is too far away.

Additionally, when the receive radius of a first access point or clientstation is large enough such that the first access point or clientstation can receive and decode packets transmitted between other accesspoints and client stations, the first access point or client station mayunnecessarily back off from transmitting packets. As a result, the firstaccess point or client station may not achieve the same transmissionthroughput that it can receive. The IEEE 802.11 standard defines carriersense multiple access with collision avoidance (CSMA/CA) mechanisms thatset out several criteria for which a WLAN access point or client stationmay check before it assumes that the wireless channel is clear. One ofthe mechanisms is physical carrier sensing which compares the signallevel on the wireless channel with an energy detect (ED) threshold. Ifan access point or client station detects a signal that is above acertain threshold, it assumes that the wireless channel is busy and willnot contend for the wireless medium. Another mechanism is the NetworkAllocation Vector (NAV) which is a virtual carrier sensing mechanismused with wireless network protocols such as IEEE 802.11. Virtualcarrier sensing is a logical abstraction that limits the need forphysical carrier sensing. The media access control (MAC) layer frameheaders contain a duration field that specifies the transmission timerequired for the frame, that is, the time during which the wirelessmedium will be busy. The stations listening in on the wireless mediumread the duration field and set their NAV, which is an indicator for astation on the duration it must defer from accessing the medium. Thus,an access point or a station whose receive radius is large compared tothat of a typical wireless device may detect packet exchanges betweenother wireless devices, and it may avoid transmitting because of theapplication of either ED or NAV mechanisms. Therefore, a device with avery sensitive receiver may contend less frequently for the medium, andtransmit less frequently, resulting in a lower throughput.

To eliminate the problems arising from asymmetric link performance of anaccess point, the receiver sensitivity of each access point can beadjusted so that the receive radius of the access point is substantiallythe same as the transmit radius of the access point. FIG. 3 shows anexample where the links for AP1 and AP2 are substantially symmetrical,that is, the transmit radius 302 and the receive radius 304 of theaccess point AP1 are substantially the same, and the transmit radius 312and the receive radius 314 of the access point AP2 are substantially thesame.

With an access point that has symmetric link performance, the situationdescribed above with respect to STA2 being located beyond the transmitradius of AP1 and yet within the receive radius of AP1 will not arise.For example, if STA2 initially associates with AP1 while located withinthe transmit radius 302 of AP1, when STA2 moves beyond the transmitradius 302 of AP1, it has also moved beyond the receive radius 304 ofAP1. This means that AP1 will no longer be able to hear transmissionsfrom STA2, nor will AP1 be able to send transmissions to STA2. As aresult, STA2 will no longer be able to associate with AP1 and willinitiate probe requests, authentication requests, or associationrequests to find and associate with another access point located closer,such as AP2 in FIG. 3. Essentially, by maintaining symmetric linkperformance for access points, client stations that establish anassociation with a first access point and subsequently move away fromthat first access point will be pushed to associate with an access pointcloser its new location.

Additionally, when an access point has symmetric link performance, theaccess point will only be able to receive probe requests and otherpackets from client stations that are within range for receiving thecorresponding probe response or other IEEE 802.11 response packets.Access points having symmetric link performance will no longer receiveprobe requests and other packets from long range client stations thatare far away. In the example of FIG. 3, STA4 is positioned outside ofboth the transmit radius 302 and the receive radius 304 of AP1, so AP1will no longer receive probe requests form STA4. STA4 will seek toassociate with a closer access point, such as AP3. The effect is toreduce or even eliminate WLAN probe response traffic to long rangeclient stations, thus, ultimately resulting in an increase in usefultraffic between an access point and near range client stations.

Moreover, an access point with a balanced link will not back off fromcontention or transmission because of a packet exchange occurringbetween two other devices that are not impacted by its transmission.This means that when an access point transmits a packet on a channelwhile another packet exchange is occurring on the same channel, if theother packet exchange is at a sufficiently distant location, the accesspoint's transmission may not impact the packet exchange at the distantlocation.

In some situations, the other packet exchange may be impacted, but theimpact is minimal. For example, if the signal to noise ratio of theother packet exchange is sufficiently high such that the intendedrecipient of the packet exchange is able to receive the information inthe packet, then the impact is considered minimal.

The access point determines whether or not it will have no impact orminimal impact on the other detected packet exchange based on twocriteria. The first criterion is that the signal strength of the otherdetected packet exchange should be less than a certain threshold. Thesecond criterion is that the selected modulation of the signal used bythe other packet exchange is at a sufficiently low data rate because ifinterference is created by the access point's transmission, a low datarate modulation, such as differential phase-shift keying (DPSK), willnot be affected as much as in the case where the modulation is occurringat a very high modulation data rate. The modulation method can bedetermined by examining the preamble of the packet which specifies themethod of modulation.

Additionally, wireless link balancing of access points in a WLAN willallow multiple WLAN networks to coexist because a link balanced accesspoint will support an increase in frequency reuse. The frequency reusefactor is the rate at which the same frequency can be used in thenetwork. When the link is not balanced, the access point may be impactedby receiving and processing some packets for which it is not desirableto receive or process, for example, a probe request, an authenticationrequest, an association request, data packets, or other types of packetsreceived from a distant client station. Alternatively or additionally,an access point that receives and processes undesirable packets couldback off from transmission of packets because criteria used by theaccess point identify the channel as being busy. When the transmit powerof a given access point is too high, that access point will increaseinterference between other access points and client stations that arebeyond the reach of that access point's receiver, resulting in areduction in the capacity of neighboring access points.

In some embodiments the access point may store a single receivethreshold, receiver settings, or maximum transmit power for a typicalclient. A typical client may be a typical cell phone, personal computer,television, or other deployed commercial devices. In these cases, theaccess point may also check the received signal strength of packetstransmitted by neighboring access points when it calculates the receivethreshold, receiver settings, or maximum transmit power. The receivethreshold, receiver settings, or maximum transmit power are alsodetermined as a function of the type of environment in which the networkequipment is deployed and the path loss between the receiver andtransmitter. The environment includes variables such as whether thenetwork is in a home or office, and also the region in which the networkis deployed, e.g., United States, Europe, and Asia, because the type ofbuilding materials vary from region to region.

For a stored receive threshold or receiver settings, the correspondingreceive radius is determined, and the transmit radius can be set to besubstantially equal to the receive radius. In some situations, thetransmit radius can be greater than the receive radius, and the networkwith the access point will perform well, although neighboring networkswith other access points may be adversely impacted. Similarly, for astored maximum transmit power, the corresponding transmit radius isdetermined, and the receive radius should be substantially the same asthe transmit radius.

In some embodiments, the access point may store and use a differentreceive radius for different clients by using software to maintain astatus for each known clients. The status includes information providedby the client station when associating with the access point, forexample, data rates supported by the client station, capabilities of theclient station, and country information. Other content of the packetexchanges and other information elements can also be used to infer thetransmit and receive capability of the client station, for example, theaccess point can determine the received power level of packets from theclient station after a packet exchange with the client station, and thisinformation is stored as part of the status of the client station. Thus,on the transmit side, the access point can choose a maximum transmitpower using TPC based on the status maintained for each known clientstation.

The access point will process or receive packets from a known clientonly if the received signal strength and/or its data rate is above acertain threshold that is calculated for that specific client. Theaccess point can identify the transmitter of a packet by reading theheader of a packet (e.g. IEEE 802.11 MAC headers). When the access pointrecognizes the source of a packet, it decides whether to process thepacket further or abort the reception of the packet. In these cases, thehardware receive sensitivity may be fixed to a particular value whilethe software threshold for processing may be changed for each clientbased on the capabilities of that client.

The access point can use a default receive threshold and transmit powerfor clients whose capabilities are not yet known to the access point.The default receive or transmit settings may be calculated for a typicalclient, and the receive power of neighboring access points may also betaken into account.

To achieve and maintain symmetric link performance for an access point,a link balancing process is performed. FIG. 4A is a flow diagramillustrating an example process of determining and setting receivesensitivity and transmit power.

At block 405, the access point receives a packet, and block 410, theaccess point identifies the client station that transmitted the packetby reading the header of the packet.

Then at decision block 415, the access point determines whether itrecognizes the transmitter, that is, whether the client station ispresently associated with the access point. If the access pointrecognizes the client station (block 415—Yes), at block 420, the accesspoint adjusts the receive sensitivity threshold for processing packetsfrom the client station. The adjustment can include adjusting hardwareprogrammable gain elements for the receive sensitivity, and/or thesoftware threshold for processing packets from the client station. Thenat block 425, the access point selects the transmission power to usewith the client station based on the stored status information for theclient station.

If the access point does not recognize the client station (block415—No), at block 430 the access point uses a default receivesensitivity threshold and default transmit power. The default receivesensitivity threshold and transmit settings are calculated usingparameters, such as transmission power and receive sensitivity, for atypical client.

Periodically, the access point can also re-adjust the receivesensitivity to the maximum receive sensitivity (receive radius) to checkfor any client stations that may be attempting to associate with theaccess point and also to ensure that it does not back off fromtransmitting packets unnecessarily when a distant packet exchange isoccurring. FIG. 4B is a flow diagram illustrating an example process ofan access point re-adjusting its receive sensitivity.

At block 450, the access point adjusts its receive sensitivity tomaximum. Then at decision block 452, the access point determines whethertransmissions to and from other access points are occurring on thechannel. The criteria for determining detection of transmissions can becustomized, for example, the access point can determine that notransmissions are detected if it detects transmissions less than acertain percentage of time, or if no transmissions are detected at allfor a specified time interval. If transmissions are detected (block452—Yes), at block 454, the access point reduces its receive sensitivityand returns to decision block 452.

If no transmissions with other access points are detected (block452—No), at block 460, the access point determines whether there areclient stations trying to associate with it. If requests to associateare not detected (block 462—No), at block 464, the access point reducesits receive sensitivity, and the process returns to block 460.

If a request to associate is detected (block 462—Yes), at decision block466, the access point determines whether it is desirable to associatewith a new client station. The decision as to whether the new clientstation attempting to associate with the access point is desirable canbe based on the signal strength of the received packet from the newstation, the modulation rate of the signal, and/or whether the data ratecan be adjusted appropriately based upon feedback between the accesspoint and the new client station for known transmitted data packets, asdescribed in the IEEE 802.11n standard. If it is not desirable toassociate with the new client station (block 466—No), at block 464, theprocess returns to block 464.

If it is desirable to associate with the new client station (block466—Yes), at block 468, the access point maintains its present receivesensitivity. Then at block 470, the access point waits a predeterminedperiod of time before the process returns to block 450.

In a similar manner, a client station can also periodically re-adjustits receive sensitivity to ensure that it does not back off fromtransmitting packets unnecessarily when a distant packet exchange isoccurring. FIG. 4C is a flow diagram illustrating an example process ofa client station re-adjusting its receive sensitivity.

At block 480, the client station adjusts its receive sensitivity tomaximum. Then at decision block 482, the client station determineswhether transmissions to and from access points other than the accesspoint the client station is currently associating with are occurring onthe channel. The criteria for determining detection of transmissions canbe customized, for example, the client station can determine that notransmissions are detected if it detects transmissions less than acertain percentage of time, or if no transmissions are detected at allfor a specified time interval. If transmissions are detected (block482—Yes), at block 484, the client station reduces its receivesensitivity and returns to decision block 482.

If no transmissions with other access points are detected (block482—No), at block 486, the client station maintains its current receivesensitivity. Then at block 486, the clients station waits apredetermined period of time, and the process returns to block 480.

Hardware Approach

FIG. 5 shows the components of a typical access point 510 that includesa wireless radio 540 and has transmit power control (TPC) adjustmentcapabilities, as defined by the IEEE 802.11h standard. The centralprocessing unit (CPU) 530 of the access point is coupled via a bus tothe radio 540 which has a transmitter with transmission gain control 545and a receiver 590. An adjustable transmission signal is sent from thetransmitter with transmission gain control 545 through a band passfilter 542, a power amplifier 544, and a low-pass filter (LPF) 546before reaching a transmit/receive switch 560. A transmitted signalstrength indicator (TSSI) from the power amplifier is also fed to ananalog to digital converter (ADC) 548 and sent back to the radio 540.

When the radio 540 is in the transmit mode, the switch 560 provides thetransmission signal to the antenna 570 for radiating into the air. Whenthe radio 540 is in the receive mode, the switch 560 provides thesignals captured by the antenna 570 to a band pass filter 582 and then alow noise amplifier (LNA) 584 before being sent to the receiver 590 inthe radio 540.

When the central processing unit (CPU) 530 of the access point receivesa TPC command from the controller 520 to adjust the radio's transmissionpower level, the transmission gain of the radio 540 is adjustedaccordingly. The transmission radius can be adjusted for each clientstation based on the capabilities of that particular client station. Theaccess point will receive some information from the client at the timeof association regarding the client station's capabilities. Afterassociation, based on data packet exchange, the rate the access pointcan transmit to the client station, and the rates and received power itreceives from the client station's transmission, the access point cancalculate the transmit power that it should use for that client station.In some implementations, the controller 520 can use a look-up table todetermine the amount of transmission gain to command the access pointCPU 530 to provide. In some implementations, the access point CPU 530can maintain the look-up table, for example, in local memory, toindependently determine the specific amount of transmission gain toprovide in the radio 540.

FIG. 6 shows example components of a wireless radio 640 of an accesspoint that includes both TPC adjustment capabilities and receiversensitivity adjustment capabilities. The CPU 630 of an access point 610that can be adjusted to have symmetrical link performance receivescommands from the controller 620 to adjust both the transmission gainand the receiver sensitivity. In addition to the traditional componentsof an access point, described above with respect to FIG. 5, the accesspoint 610 can include a receive noise figure control (RNFC) 650positioned before the low-noise amplifier 655. Alternatively oradditionally, the access point 610 can include an external receive gaincontrol 660 positioned after the low-noise amplifier 655. Both the RNFC650 and the external receive gain control 660 are adjustable attenuatorscontrolled by a receiver with receiver gain control 670 in the radio640, and the receiver gain control 670 is responsive to commands fromthe controller 620. In some implementation, the CPU 630 calculates thereceive gain that is optimum for a particular client station and canstore the information in a look-up table. In some implementations, thecontroller 620 can use a look-up table to determine the amount ofreceive gain to command the access point CPU 530 to provide. In someimplementations, the access point CPU 630 can maintain the look-uptable, for example, in local memory, to independently determine thespecific amount of receive gain to provide in the radio 640.

While FIG. 6 shows example components of a wireless radio of an accesspoint, the example components of the wireless radio can also be used ina client station, except that the CPU 630 operates independently of acontroller 620. Instead, the CPU 630 can perform calculations todetermine the appropriate transmission gain and receive sensitivity useto communicate with an access point.

Software Approach

Some manufacturers of wireless LAN chipsets that include radiocomponents provide for a programmable gain amplifier that can becontrolled externally, using external digital or analog signals. Thus,rather than using hardware external to the LAN chipset, the gain insidethe LAN chipset can be adjusted using software. Some wireless chipsetshave all or part of the radio frequency (RF) functionality included inthem. The RF functionality includes receive components such as low-noiseamplifiers (LNA), filters, switches and other programmable or fixed gainelements. The transmit RF functionality includes power amplifiers,filters, switches, and other programmable or fixed gain elements.

When the controller sends a command to the CPU of the access point toadjust the receiver sensitivity, the CPU can either increase theattenuation of the received signal to decrease receiver sensitivity,thereby decreasing the receive radius, or decrease the attenuation ofthe received signal to increase the receiver sensitivity and thecorresponding receive radius. In the case of a client station, the CPUof the client station can perform calculations to determine theappropriate receiver sensitivity use to communicate with an accesspoint.

In some other software controlled embodiments, the receiver may notchange the gain at the receiver side but it may choose to control thereceive power level or receive modulation level at which it receives orprocesses a certain packet. The receive power level or receivemodulation level may change for different clients. Since the accesspoint will know the identity of the client after processing the physical(PHY) header and when it is processing the MAC header, it can choosewhat to do with a packet based on its receive power and its identityafter it processes the relevant fields in the MAC header.

In some other embodiments, the access point or the client station maychoose to use a combined method that changes the programmable gainelements and also applies thresholds at which it receives or processes apacket.

In addition to the receive threshold used for receiving and processingpackets, the software may also use a threshold for which it holds NAV orfor which it applies ED. Adjustable thresholds for NAV or ED help adjustthe access point's behavior in accessing the medium while there isinterfering traffic from neighboring access points on the same wirelesschannel. The access point may choose to transmit a packet when it seessome level of interference. The level of interference the access pointcan tolerate will depend on the capability of the access point, theclient station, and the rate that the access point is using to transmitto a client station and/or the rate that a client station uses totransmit to the access point. Based on this concept, the access pointcan choose to support an interference channel. Similarly, a clientstation can also choose to support an interference channel.

FIG. 7 is an example of an architecture of the access point 710configured, for example, to receive commands from a controller to adjustthe transmit power and the receive sensitivity of the access point. Inthe example of FIG. 7, the access point 710 includes a CPU 720, a radio750, and a memory 760. The CPU 720 can further include a receivesensitivity controller module 730 and a transmit power controller module740. The CPU 720 and all of the elements included within the CPU 720 areimplemented by using programmable circuitry programmed by softwareand/or firmware, or by using special-purpose hardwired circuitry, or byusing a combination of such embodiments. Additional or fewer elementscan be included in the CPU 720 and each illustrated component. As usedherein, a “module,” includes a general purpose, dedicated or sharedprocessor and, typically, firmware or software modules that are executedby the CPU 720. Depending upon implementation-specific or otherconsiderations, the module can be centralized or its functionalitydistributed. The module can include general or special purpose hardware,firmware, or software embodied in a computer-readable (storage) mediumfor execution by the CPU 720.

When the CPU 720 receives commands from a controller to increase ordecrease the transmit power of the access point, the transmit powermodule 740 increases or decreases the transmit power gain using hardwarein the radio 750 such that the power of the transmitted signals areappropriately adjusted responsive to the controller commands.

Additionally or alternatively, the transmit power module 740 cancalculate the transmit power that it should use for a particular clientstation based upon the capabilities of the client station received atthe time of association, the rate at which the access point can transmitpackets to the client station, and the rate and received power ofpackets received from the client station. Based on the calculation, thetransmit power module 740 can adjust the transmit power of the accesspoint.

When the CPU 720 receives commands from the controller to increase ordecrease the receive sensitivity of the radio 750, the receivesensitivity controller module 730 sends digital or analog signals,depending upon the particular signals expected by the wireless LANchipset, to adjust a programmable gain to change the receive sensitivityappropriately.

Additionally or alternatively, the receive sensitivity controller module730 can adjust the receive power level threshold or received modulationlevel threshold at which it receives or processes packets for eachclient.

In some implementations, the memory 760 is configured to store atransmit power gain look-up table that can be accessed by the transmitpower controller module 740 to determine how much to adjust the transmitpower gain hardware in response to the controller's commands. In someimplementations, the memory 760 is configured to store a receivesensitivity look-up table that can be accessed by the receivesensitivity controller module 730 to determine the signals to send tothe wireless LAN chipset to adjust the programmable gain or attenuation.

While FIG. 7 shows an example architecture of an access point, the sameexample architecture also applies to a client station, except that theclient station CPU 720 does not receive commands from a controller toadjust the transmit power or the receive sensitivity of the clientstation, rather the transmit power module 740 calculates the transmitpower that should be used for a particular client station, and thereceive sensitivity controller module 730 adjusts the receive powerlevel or received modulation level at which the client station receivesor processes packets for each client.

Maintaining Symmetric Link Performance

FIG. 8 is a flow diagram illustrating an example process of maintainingan access point with symmetric link performance once the symmetry hasbeen established. At decision block 810, the controller determineswhether a TPC adjustment is needed for a particular access point. Forexample, a TPC adjustment may be needed to reduce interference betweenwireless devices or to limit power consumption of the access point. Ifno TPC adjustment is needed (block 810—No), the process remains atdecision block 810.

If a TPC adjustment is needed (block 810—Yes), at block 815, thecontroller sends a command to the access point to adjust thetransmission power level. Then at block 820, the controller determinesthe corresponding receiver sensitivity adjustment for the access point,and at block 825, the controller sends the command to the access pointto adjust the receiver sensitivity accordingly. The process then returnsto decision block 810.

Methods and systems for controlling the transmit power and the receivesensitivity of an access point to provide symmetrical link performancehas been described. It will be appreciated by those of ordinary skill inthe art that the concepts and techniques described herein can beembodied in various specific forms without departing from the essentialcharacteristics thereof. The presently disclosed embodiments areconsidered in all respects to be illustrative and not restrictive. Thescope of the invention id indicated by the appended claims, rather thanthe foregoing description, and all changes that come within the meaningand range of equivalence thereof are intended to be embraced.

What is claimed is:
 1. An apparatus comprising: a radio configured totransmit radio frequency (RF) signals to a wireless device and toreceive RF signals from the wireless device; a receive gain controlconfigured controllable to adjust a receive radius to receive RF signalsfrom the wireless device, or a module controllable to adjust a thresholdfor receiving or processing RF signals, based on whether the wirelessdevice is within the receive radius of the radio; and a processorconfigured to perform operations comprising: upon receiving a packet,identifying a transmitter of the packet; and upon determining that thetransmitter is known, adjusting the threshold for receiving orprocessing RF signals based on parameters specific to the identifiedtransmitter.
 2. The apparatus of claim 1, wherein the adjustment isbased upon a received signal strength of the packet and/or a transmitteddata rate of the packet.
 3. The apparatus of claim 1, furthercomprising: a transmit gain control controllable to adjust a power ofthe transmitted RF signals to reach the wireless device based on whetherthe wireless device is within a transmit radius of the radio.
 4. Theapparatus of claim 3, wherein the processor is further caused toperform: upon determining that the transmitter is known, adjusting thepower of transmitted RF signals to reach the transmitter based upon theparameters specific to the identified transmitter.
 5. The apparatus ofclaim 3, wherein the parameters specific to the identified transmitterincludes information provided by the transmitter when associating withthe apparatus and/or the received power level of the packet from thetransmitter.
 6. The apparatus of claim 3, wherein the receive radius ofthe apparatus is adjusted to become substantially equal to the transmitradius of the apparatus.